Mercurial > hg > sv-dependency-builds

annotate src/fftw-3.3.3/doc/html/Dynamic-Arrays-in-C.html @ 10:37bf6b4a2645

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Add FFTW3
author Chris Cannam
date Wed, 20 Mar 2013 15:35:50 +0000
parents
children
rev   line source
Chris@10 1 <html lang="en">
Chris@10 2 <head>
Chris@10 3 <title>Dynamic Arrays in C - FFTW 3.3.3</title>
Chris@10 4 <meta http-equiv="Content-Type" content="text/html">
Chris@10 5 <meta name="description" content="FFTW 3.3.3">
Chris@10 6 <meta name="generator" content="makeinfo 4.13">
Chris@10 7 <link title="Top" rel="start" href="index.html#Top">
Chris@10 8 <link rel="up" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format">
Chris@10 9 <link rel="prev" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C" title="Fixed-size Arrays in C">
Chris@10 10 <link rel="next" href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way" title="Dynamic Arrays in C-The Wrong Way">
Chris@10 11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
Chris@10 12 <!--
Chris@10 13 This manual is for FFTW
Chris@10 14 (version 3.3.3, 25 November 2012).
Chris@10 15
Chris@10 16 Copyright (C) 2003 Matteo Frigo.
Chris@10 17
Chris@10 18 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@10 19
Chris@10 20 Permission is granted to make and distribute verbatim copies of
Chris@10 21 this manual provided the copyright notice and this permission
Chris@10 22 notice are preserved on all copies.
Chris@10 23
Chris@10 24 Permission is granted to copy and distribute modified versions of
Chris@10 25 this manual under the conditions for verbatim copying, provided
Chris@10 26 that the entire resulting derived work is distributed under the
Chris@10 27 terms of a permission notice identical to this one.
Chris@10 28
Chris@10 29 Permission is granted to copy and distribute translations of this
Chris@10 30 manual into another language, under the above conditions for
Chris@10 31 modified versions, except that this permission notice may be
Chris@10 32 stated in a translation approved by the Free Software Foundation.
Chris@10 33 -->
Chris@10 34 <meta http-equiv="Content-Style-Type" content="text/css">
Chris@10 35 <style type="text/css"><!--
Chris@10 36 pre.display { font-family:inherit }
Chris@10 37 pre.format { font-family:inherit }
Chris@10 38 pre.smalldisplay { font-family:inherit; font-size:smaller }
Chris@10 39 pre.smallformat { font-family:inherit; font-size:smaller }
Chris@10 40 pre.smallexample { font-size:smaller }
Chris@10 41 pre.smalllisp { font-size:smaller }
Chris@10 42 span.sc { font-variant:small-caps }
Chris@10 43 span.roman { font-family:serif; font-weight:normal; }
Chris@10 44 span.sansserif { font-family:sans-serif; font-weight:normal; }
Chris@10 45 --></style>
Chris@10 46 </head>
Chris@10 47 <body>
Chris@10 48 <div class="node">
Chris@10 49 <a name="Dynamic-Arrays-in-C"></a>
Chris@10 50 <p>
Chris@10 51 Next:&nbsp;<a rel="next" accesskey="n" href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html#Dynamic-Arrays-in-C_002dThe-Wrong-Way">Dynamic Arrays in C-The Wrong Way</a>,
Chris@10 52 Previous:&nbsp;<a rel="previous" accesskey="p" href="Fixed_002dsize-Arrays-in-C.html#Fixed_002dsize-Arrays-in-C">Fixed-size Arrays in C</a>,
Chris@10 53 Up:&nbsp;<a rel="up" accesskey="u" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>
Chris@10 54 <hr>
Chris@10 55 </div>
Chris@10 56
Chris@10 57 <h4 class="subsection">3.2.4 Dynamic Arrays in C</h4>
Chris@10 58
Chris@10 59 <p>We recommend allocating most arrays dynamically, with
Chris@10 60 <code>fftw_malloc</code>. This isn't too hard to do, although it is not as
Chris@10 61 straightforward for multi-dimensional arrays as it is for
Chris@10 62 one-dimensional arrays.
Chris@10 63
Chris@10 64 <p>Creating the array is simple: using a dynamic-allocation routine like
Chris@10 65 <code>fftw_malloc</code>, allocate an array big enough to store N
Chris@10 66 <code>fftw_complex</code> values (for a complex DFT), where N is the product
Chris@10 67 of the sizes of the array dimensions (i.e. the total number of complex
Chris@10 68 values in the array). For example, here is code to allocate a
Chris@10 69 5&nbsp;&times;&nbsp;12&nbsp;&times;&nbsp;27 rank-3 array:
Chris@10 70 <a name="index-fftw_005fmalloc-121"></a>
Chris@10 71 <pre class="example"> fftw_complex *an_array;
Chris@10 72 an_array = (fftw_complex*) fftw_malloc(5*12*27 * sizeof(fftw_complex));
Chris@10 73 </pre>
Chris@10 74 <p>Accessing the array elements, however, is more tricky&mdash;you can't
Chris@10 75 simply use multiple applications of the &lsquo;<samp><span class="samp">[]</span></samp>&rsquo; operator like you
Chris@10 76 could for fixed-size arrays. Instead, you have to explicitly compute
Chris@10 77 the offset into the array using the formula given earlier for
Chris@10 78 row-major arrays. For example, to reference the (i,j,k)-th
Chris@10 79 element of the array allocated above, you would use the expression
Chris@10 80 <code>an_array[k + 27 * (j + 12 * i)]</code>.
Chris@10 81
Chris@10 82 <p>This pain can be alleviated somewhat by defining appropriate macros,
Chris@10 83 or, in C++, creating a class and overloading the &lsquo;<samp><span class="samp">()</span></samp>&rsquo; operator.
Chris@10 84 The recent C99 standard provides a way to reinterpret the dynamic
Chris@10 85 array as a &ldquo;variable-length&rdquo; multi-dimensional array amenable to
Chris@10 86 &lsquo;<samp><span class="samp">[]</span></samp>&rsquo;, but this feature is not yet widely supported by compilers.
Chris@10 87 <a name="index-C99-122"></a><a name="index-C_002b_002b-123"></a>
Chris@10 88 <!-- =========> -->
Chris@10 89
Chris@10 90 </body></html>
Chris@10 91